Bar codes have been used in a wide variety of applications as a method for conveying information about products. For example, bar codes are frequently applied to products to identify the product and the price of the product. This information is used by point-of-sale terminals, quality control systems, and inventory control systems. Bar codes are also frequently used in personnel access systems and mailing systems.
Bar codes typically comprise a series of black lines. The width and spacing between the lines corresponds to a code. There are many different kinds of bar codes known in the art. In each bar code system, an alphanumeric character or other symbol is represented by a unique pattern of lines. The bar code is read by scanning the bar code with a beam of visible, infrared, or ultraviolet light. The lines of the bar code absorb a portion of the light and a portion of the light is reflected by the background of the bar code, or vice versa. The light reflected from the bar code is detected by the scanner, converted into an electrical signal and then decoded.
Most bar codes are printed with inks that are visible to the naked eye. One disadvantage of visible bar codes is that the visible bar code takes up space on products and labels, often detracting from their appearance. Inks that are not visible to the naked eye have also been used in the past to print bar codes. Bar codes printed in invisible inks can be printed over other information on labels, thereby saving space on the product, package, or label. Also, invisible bar codes can be used to authenticate products or documents and to prevent or hinder counterfeiting. For example, invisible bar codes can be printed on stock certificates, bonds, currency, and licenses. Unlike visible bar codes, invisible bar codes are difficult to forge because special inks are required that may not be generally available.
When bar codes are printed in invisible inks, there is a problem in locating the code so that it can be scanned. Viewers or scanners for reading invisible bar codes tend to be large and bulky and therefore not suitable for use as portable, hand-held scanners or viewers. Accordingly, there is a need for a portable scanner or viewer that is capable of reading invisible bar codes or other markings.